The Berklee School of Music alumni, who started making music together in a Ditmas Park share house a decade ago, also share their innermost thoughts, funnelling intimate details into songs that simultaneously borrow from and deconstruct classic girl group pop.

“We’re so fortunate because we’re a partnership and we also see every part of each other’s lives, so we’re able to be a voice of reason or at least have some sort of objective ear and eye in each other’s lives.

“I’m watching her experiences and Holly’s watching mine,” she adds. “There’s no closer writing companion you could have.”

While there’s no psychopathic Jennifer Jason Leigh character in Lucius, the group’s second album Good Grief, released in 2016, does feature Gone Insane, Almighty Gosh and other fragile songs written during an emotional purge.

“We had toured (acclaimed 2013 debut album Wildewoman) in a 12-passenger van with five or more of us for about three years and coming off the end of that was when we started writing Good Grief,” Wolfe says. “It was rough.”

“Your relationships are strained,” Laessig offers. “Every kind of relationship you have is strained because you’re constantly moving and there’s never a moment to reflect, so when you are given that moment it’s kind of like, blah, purging.”

That closeness is reflected in the pair’s incredibly tight harmonies. Their vocal prowess has led to collaborations with David Byrne, Jeff Tweedy, Mavis Staples, John Legend and, most significantly, Roger Waters.

Lucius’ star turn at the Perth Festival follows the final date of their Australasian tour with the Pink Floyd legend.

The “ongoing collaboration and friendship” began when Laessig and Wolfe performed with Waters at the Newport Folk Festival in 2015.

The highlight, so far, has been the Desert Trip festival two years ago in California, where they shared the stage with the Rolling Stones, Bob Dylan, Paul McCartney, Neil Young and the Who.

“It was probably the most proud I’ve been to take my parents to a gig,” Laessig says. “To be able to share the stage with all those artists that mean so much to us ... it was a really, really special experience.”

Waters has been a “a very generous and awesome mentor and boss”.

“He really wants us as Lucius, not in the corner singing background vocals,” Laessig adds. “We’re standing right beside him and it’s a really special experience.”

Wolfe says that touring and recording with Waters and other legends has influenced the way they approach their music, in particular staging and other visual accompaniments.

When we spoke, Lucius — the band is rounded out by guitarist Peter Lalish — had finished writing for their third album and were about to step into the studio.

“It’s always a really adventurous time when the four of us can get together in a room and listen to these songs and see how we can create a world around them,” Laessig says.

“As we’ve been writing it,” Wolfe adds, “we’ve been thinking about it as a film.”

With Waters rocking Perth Arena on February 20, two days before Lucius play the Perth Festival with English folk-rock trio the Staves, the sisters of song have a few spare days in town.

They love good food, nature, people-watching and art ... or as Wolfe puts it: “We are open to suggestions.”

Lucius and the Staves play the Chevron Gardens on February 22. Tickets from perthfestival.com.au.